SMT Design Rule Types Available for PCB Layout in Altium Designer
The design rules of the SMT category are described below.
SMD To Corner
Default Rule: not required
This rule specifies the minimum distance from the edge of a surface mount pad to the first routing corner.
Constraints
Distance - the value for the minimum permissible distance from the SMD pad edge to the start of the first routing corner.
Rule Application
Online DRC and Batch DRC, and Interactive Routing.
Notes
-
The interactive router will obey this rule by maintaining a straight pad exit trace emanating from the pad center on any allowed "entry angle" (see SMD Entry rule), at least to the distance specified.
- Once the pad has been exited, the route is kept away from the pad. The software does not allow the route to re-enter the pad and then re-exit without regard to the SMD rules.
- SMD rules are ignored if the pad exit is blocked (they are already ignored during pad entry in this situation). Note that if there is a pad exit available that does not violate the SMD to corner rule, that exit will be used.
- Miters are not created in violation of SMD rules. The software favors the SMD to corner rule over the miter, allowing the miter to collapse to zero if required.
- Stubs that follow the SMD rules are created in Any Angle routing mode. In this mode, once the first track segment has been placed arcs will be included in the corners. If you need an arc in the first corner, place the exit stub before attempting to create a corner.
- When using the Interactive Differential Pair Routing tool, note that coupling the differential pair has priority. Therefore, the SMD To Corner and SMD Entry design rules might not work as expected. If strict respect for these rules is required when routing a differential pair, use the Quick Differential Pair Routing tool.
SMD To Plane
Default Rule: not required
This rule specifies the maximum routing length from the center of a surface mount pad to the center of the pad/via connecting to a power plane.
Constraints
Distance - the value for the maximum permissible distance from SMD pad to pad/via connecting to the power plane.
Rule Application
Online DRC and Batch DRC.
SMD Neck-Down
Default Rule: not required
This rule specifies the maximum ratio of the track width to the SMD pad width, expressed as a percentage.
Constraints
Neck-Down - the percentage value for the maximum permissible ratio of track width to SMD pad width. Entering a larger value will allow for the use of greater width track.
Rule Application
Online DRC and Batch DRC.
SMD Entry
Default Rule: not required
This rule specifies the direction(s) a track can enter, or exit, an SMD pad.
Constraints
- Any Angle – if enabled, the track can enter/exit the pad at any angle, and at any point along its edge.
- Corner – if enabled, the track can enter/exit through a pad corner.
- Side – if enabled, the track can enter/exit at 90 degrees on either side of the pad. The longer edge of the pad is considered the side, note that the side option is only applied if the
Side length > 2x End length
. For example, if the pad is2mm x 1mm
then the side option is ignored (all sides are treated as ends). If the pad is2.1mm x 1mm
then the side option is applied.
Rule Application
Online DRC, Batch DRC, and Interactive Routing.
Notes
- The rule applies to surface mount pads only, that is, a pad defined on a single copper layer.
- The end of the pad is determined from the pad dimensions, the ends are the shorter edges.
- Pads can always be entered from either end (the shorter edge)
- The rule is applied on both routing out of the pad (exit) and into the pad (entry).
-
The rule works in harmony with the SMD To Corner design rule, configure both to ensure neat SMD routing.
- Once the pad has been exited, the route is kept away from the pad. The software does not allow the route to re-enter the pad and then re-exit without regard to the SMD rules.
- SMD rules are ignored if the pad exit is blocked (they are already ignored during pad entry in this situation). Note that if there is a pad exit available that does not violate the SMD to corner rule, that exit will be used.
- Miters are not created in violation of SMD rules. The software favors the SMD to corner rule over the miter, allowing the miter to collapse to zero if required.
- Stubs that follow the SMD rules are created in Any Angle routing mode. In this mode, once the first track segment has been placed arcs will be included in the corners. If you need an arc in the first corner, place the exit stub before attempting to create a corner.
- When using the Interactive Differential Pair Routing tool, note that coupling the differential pair has priority. Therefore, the SMD To Corner and SMD Entry design rules might not work as expected. If strict respect for these rules is required when routing a differential pair, use the Quick Differential Pair Routing tool.